1. Field of the Invention
The present invention relates to a turret punch press, and more specifically to a die exchange section of a turret punch press for punching plate-shaped work.
2. Description of the Related Art
In the turret punch press, in general, a body frame is provided as a base, and a pair of disk-shaped upper turret and lower turret (both diameters are roughly equal to each other) are mounted on the body frame so as to be opposed to each other. On the upper turret, a number of exchangeable punches are arranged in a number of punch mount holes formed at regular angular intervals along the circumferential direction of the upper turret. Similarly, on the lower turret, a number of exchangeable dies are arranged in a number of die mount holes formed also at regular angular intervals along the circumferential direction of the lower turret. A desired mated pair of the punch and die is selected from among a number of pairs of the punches and dies, and the selected pair is located in a punching area. For the above-mentioned selection of the desired pair of the punch and die, a turret rotating servomotor is mounted for the upper turret and the lower turret, respectively.
Now, in the case of the upper turret, since the upper side of the upper turret is largely open, a punch fitted to a punch mount hole can be easily exchanged from above with the use of an appropriate automatic punch exchanging apparatus. In the case of the die, on the other hand, since the vertical clearance (i.e., gap) between the upper turret and the lower turret is relatively small, it is difficult to automatically exchange a die fitted to a die mount hole from above, with the result that the die is usually exchanged manually by a worker.
To overcome this problem, the same applicant has already proposed such a turret punch press that the upper turret is dislocated away from the die exchange area so that a die fitted to a die mount hole can be exchanged automatically from above by use of an automatic die exchanging apparatus, as disclosed in U.S. Ser. No. 08/006,941. This turret punch press is characterized in that the size of the upper turret is formed smaller than that of the lower turret and further the rotational axis of the upper turret is located near the side of the punching area, as compared with the rotational axis of the lower turret. In the turret punch press already proposed by the same applicant, however, since the die feeding cylinder for feeding the die from the die holder portion of the exchange arm to the die mount hole is provided on the exchange arm, a large load is inevitably applied to the die exchange arm, in addition to the weight of the die exchange arm. As a result, it is difficult to increase the rotational speed of the die exchange arm and thereby to improve the locating precision of the die exchange arm, thus resulting in a problem in that the die exchange work efficiency is lowered.